What is the actual definition of "Render"
It will depend a bit on whether you're trying to explain this to a layman, trying to draft a professional description (like for LinkedIn or other professional profile), or just trying to generally understand the technical definition. If you can add this info to your question, it'd be helpful.
That being said...
The Merriam-Webster definition is actually useful in beginning the description, particularly definitions 4 &amp; 5:

4a (1) :  to cause to be or become b (1) :  to reproduce or represent by artistic or verbal means :  depict (2) :  to give a performance of (3) :  to produce a copy or version of (4) :  to execute the motions of 
5:  to direct the execution of

Wikipedia's definition is a little bit more accessible:

Rendering is the process of generating an image from a 2D or 3D model (or models in what collectively could be called a scene file) by means of computer programs.

But the most useful description would probably be the one that I (very officially) just came up with:

Rendering is the process of turning the digital description of a scene, at a particular moment in time, into an image. Rendering is a lot like taking a photograph of a scene that only exists in the computer. Scenes are described in simplified, human-accessible ways, and the computer then uses that description to calculate all of the implied (non-explicit) things to determine the color of each pixel in the entire image.

A very useful analogy in describing this process is telling someone else what to draw. I could write a letter to someone, describing what I wanted them to draw (without using any pictures), and the process of them reading what I wrote and turning it into a picture is almost EXACTLY the same as rendering in Blender (in fact, in the art world, the physical process of putting marks on paper is actually called 'rendering'). In fact, it's so similar that I could even add a tiny drawing of what the bumps on one of the bricks looks like, and that's a LOT like using an image texture in Blender.
The ONLY difference between this and rendering with Blender is that humans can make assumptions, but Blender can't. The letter could say &quot;a double-hung aluminum window with 6 equal panes,&quot; and a person would have a very clear idea of what that looks like, but Blender would need a LOT more information.
I hope that helps!